Cheese-producing textile machines, for example automatic cheese winders, are known, for example, from German Patent Publication DE 195 12 891 A1 or DE 195 20 133. The work stations of these textile machines, which are arranged next to each and are all of the same type, are serviced by an automatically operating service unit, for example a cheese changer.
More specifically, the cheese changer transports finished cheeses from the winding installation of a work station to a cheese transporting device which extends the length of the machine and is arranged behind the winding installations, and the cheese changer thereafter places a fresh empty bobbin from an intermediate storage assigned to the work station into the winding installation.
In order to prevent difficulties in the course of the transfer of the cheeses to the transport device which can occur, for example, if there already is a cheese on the respective place of deposit, the cheese changer in accordance with German Patent Publication DE 195 12 891 A1 has a sensor device in the form of a light scanner. The cheese transport device is scanned by this sensor device prior to initiating the cheese changing process. Thus, the cheese change is started only if it is ascertained by means of the sensor device that the respective place of deposit on the cheese transport device is empty.
A comparable sensor device is also described in German Patent Publication DE 37 31 125 A1 in connection with an open-end spinning machine. The movable service unit of this known textile machine also has a sensor device for scanning a cheese transporting device. Here, the sensor device is either embodied as a mechanical feeler device or as a photo-electrical sensor element.
However, the known sensor devices for cheese changing units were not entirely satisfactory in everyday spinning operations or have various disadvantages. For example, with mechanical sensor devices there is the danger that the relatively sensitive cheese is damaged by the mechanical feeler arm. Furthermore, such devices can cause or promote the creation of damaging slack threads.
Although these disadvantages can be avoided by photo-electrical sensor devices since such sensor devices operate contact-free, it is known that optical devices are very sensitive to dirt. Since in spinning mills it is hardly possible to avoid airborne fibers and dust contaminated with softener, photo-electrical sensor devices require regular careful maintenance, since otherwise it is hardly possible to prevent errors in the functioning of the sensor devices.
It is furthermore disadvantageous in connection with photo-electric light scanners that such sensor devices are strongly dependent on the coloration of the object to be scanned. Thus, light-colored objects are essentially more dependably detected than dark-colored objects. Matte-black objects can almost not be detected.
In addition, other sensor devices which operate without physical contact are known from general mechanical engineering in the form of so-called ultrasonic proximity switches. Such ultrasonic proximity switches are able to detect objects at distances between approximately 6 and 600 cm. Ultrasonic proximity switches are commercially available components, whose function is explained, for example, in a prospectus of the Siemens company (Siemens NS 3, 1991).
However, these ultrasonic proximity switches have the physical disadvantage that the speed with which the sound waves are propagated is a function of various environmental conditions, for example the air temperature, humidity and air pressure. Depending on the location of employment of the ultrasonic proximity switches, these environmental conditions can vary greatly. However, as a rule, the environmental conditions change only in a limited way and mostly relatively slowly at the respective locations of use.
In order to be able to compensate for these climatic conditions, the known ultrasonic proximity switches are equipped with additional temperature sensors and compensating devices, which clearly make the known ultrasonic proximity switches more expensive.
Although the employment of electro-acoustic sensor devices in connection with textile machines is basically known from German Patent Publication DE 39 32 665 A1, such known devices are not comparable with the subject of the present invention.
German Patent Publication DE 39 32 665 A1 relates to a device for the protection of people and protection against collisions of an automatically operating service unit of a ring-spinning machine. Here, the service unit has an electro-acoustic converter at the respective ends, which supplies a dual transmission sound signal and is connected with an electronic control unit. In the process, a sound measuring signal is radiated in the direction of travel, while a sound reference signal is directed to a reference reflector, for example the shop floor. The electronic control device supplies a recognition signal, or initiates a reversal of the traveling direction of the service unit if a sound signal is received prior to the end of the reference travel time, since such a sound signal suggests an obstacle in the path of the service unit. If no sound signal occurs until the end of the travel time of the reference signal, the control unit signals an error and stops the service unit.